Testing processes with junit in spring

Flowable Engine
2

After looking at your tutorial, I tried to test my processes in similar way, but in Java. However, I am unable to mock the service task. My test runs the actual service task instead of the mock. I have also built TestConfiguration for MockExpressionManager, but still does not work.

Test

@RunWith(SpringRunner.class)
@SpringBootTest
public class PortfolioProcessTest {

@Autowired
private RuntimeService runtimeService;

@Test
public void startPortfolioProcess(){
    prepareEnv();
    this.runtimeService.startProcessInstanceByKey("portfolioReconfigurationProcess",getProcessStartVariable());
}

public void prepareEnv(){
     MailService mockMailService = mock(MailService.class);
     when(mockMailService.sendMail()).thenReturn("Sending Mail");
     Mocks.register("rejectMailPms",new RejectMailPms(mockMailService));
}

ServiceTask
@Service
public class RejectMailPms {

MailService mailService;

@Autowired
public RejectMailPms(MailService mailService){
    this.mailService = mailService;
}

public void sendMail(){
    System.out.println(mailService.sendMail());
}

}

MailService
@Service
public class MailService {

public String sendMail(){
    return  null;
}

}

@Configuration
public class TestConfiguration {

@Bean
public EngineConfigurationConfigurer<SpringProcessEngineConfiguration> flowableTestSpringProcessEngineConfig(){
    return new MyConfigurer();
}

}

public class MyConfigurer implements EngineConfigurationConfigurer {

public void configure(SpringProcessEngineConfiguration processEngineConfiguration) {
    // advanced configuration
    processEngineConfiguration.setExpressionManager(new MockExpressionManager());
}

}